I just cleaned and refilled hot tub (same thing for 11 years) This time the back jets did not engage after filling up. Front jets work great. Is it possible to have an airlock on half the jets? Or could there be a fuse issue? It is heating up now, and I have tried the hose in the filter and the plunger. I will have to work on it tomorrow, as it is dark out now, but any suggestions?